A plasma processing apparatus has been used in a semiconductor device manufacturing process for etching a substrate (for example, a semiconductor wafer) with plasmatized gas acting on the substrate. Such a plasma processing apparatus includes a capacitive coupling plasma processing apparatus which has an upper electrode and a lower electrode facing each other in a process chamber and generates plasma by applying high-frequency power across these electrodes. Another plasma processing apparatus has the above-described structure and controls the plasma density with a magnetic field.
The above-described plasma processing apparatus can generate the plasma sheath which has different thicknesses between an area above the substrate and an area above and outside the substrate because a peripheral area and an outside area of the substrate are different in structure and material. The thickness difference in the plasma sheath causes an interface of the plasma sheath (interface between the plasma sheath and the plasma) to have a level difference to have a slanting portion at the boundary between the lower and higher-level portions. Ions are obliquely incident on the slanting portion, resulting in tilting which is a tilting etching state. A measure to flatten the interface of the plasma sheath is to surround the outer periphery of the substrate by a focus ring made of, for example, Si or SiC. Another measure to flatten the interface of the plasma sheath to prevent the tilting is to change the thickness and material of the focus ring or apply a high-frequency bias to the focus ring itself.